The present invention, in some embodiments thereof, relates to inkjet printing techniques and, more particularly, but not exclusively, to improved processes and compositions for inkjet printing of high resolution color and stretchable images on a dyed synthetic textile substrate.
Polyester fabrics are used widely for preparing sport apparel, and are very popular as dry-fit garments. The polyester fibers which are intrinsically colorless or white are dyed using dispersed dyes. The technique of introducing dyes into the polyester fibers is effected by heating the fabric in aqueous dispersion of the dye at elevated temperatures raging 90-150° C. At the elevated temperatures the polyester fibers are loosed while the dye enters the fibers' polymer and on cooling remains entangled therein.
Inkjet printing on polyester-based fabrics is widely recognized as limited by dye migration or bleeding, which occurs in polyester garments when a dispersed dye in the polyester fiber is heated to temperatures in excess of 130° C., causing the dye entanglement process to reverse and the dye to migrate, a phenomenon known as dye migration or vagrant dye, which is assumed to involve dye sublimation. When plastisol-based inks, used in screen-printing, and inkjet ink compositions (typically aqueous-based pigment dispersed in acrylic emulsion, and/or styrene acrylic emulsion, and/or PVC acrylic emulsion and/or polyurethane emulsion), are heated post-printing to temperatures higher than 130° C., (most inks are cured at 130-160° C.), these dyes are released into the ink causing a discoloration of the cured ink, while higher temperatures cause more severe migration. Film-forming inks are the most affected since they act, when heated, as a media for the diffusion (migration) dye molecules, which diffuse (migrate) through the ink film even after it has been cured (dye molecules can even migrate to the surface of ink through air). This dye migration effect is more damaging with clear gel prints or solid white prints.
U.S. Pat. Nos. 3,940,247, 3,957,427, 4,132,522, 4,758,243, 5,350,530, 5,733,341, 5,773,372, 6,331,352, 7,320,712, 8,349,427 and 8,859,461, which are incorporated herein by reference as if fully set forth herein, teach various methods for controlling dye migration in synthetic fabrics such as polyester.
A technology of synthesizing nylon and polyester with acidic functional groups as part of the polymer strands has been developed in the last decades. The existence of acidic functional groups enables dyeing of nylon, lycra and polyester fibers and fabrics, while reacting chemically cationic dyes with the acidic groups attached to the fibers polymers.
However, the problem of dye migration is still present even when printing on polyester fabrics dyed with cationic dyes, presumably since water-based inkjet compositions are typically basic, and the basic species in the inks may displace the cationic dye, leading to dye migration.
A family of dispersed pigment-based digital inks, suitable for printing on dark and/or light colored, absorptive and/or stretchable fabrics, as well as inkjet printing methodologies for printing images on such substrates, have been disclosed in, for example, U.S. Patent Application Nos. 20040252173, 20070103528, 20070103529, 20070104899, 20110032304, 20120040148 and 20140036014, U.S. Pat. No. 8,540,358 and International Patent Application Nos. WO 2005/115089, WO 2005/115761, WO 2014/076705 and WO 2011/018786, each of which being incorporated by reference as if fully set forth herein. These ink compositions and printing processes are based on a chemical and/or physical property of the ink components, which can be selected so as to coagulate or precipitate upon contact with another substance on the surface of the substrate. In some of the aforementioned dispersed pigment-based digital inkjet ink composition, the immobilization is afforded by using an acidic immobilization composition, while the subsequent step comprises printing a colored ink composition which is basic and sensitive to the acidic condition now effected on the substrate, such that the dispersed pigment coagulates and becomes immobilized until it is cured be heat. This coagulate or precipitate, or otherwise immobilization of the ink droplet, affords several major achievements—the ink is not absorbed by the substrate in case of textile and other absorptive materials, hence there is very minimal penetration and crossing-over of ink into the fabric and its back-side; the droplets preserve their original size and shape of microscopic droplets by not spreading over and/or into the substrate, thereby affording a sharper image and better color definition; and the ink forms a film over the substrate, which once cured can be selected so as to be stretchable and breathing, allowing the formation of a digital image on a stretchable substrate without sacrificing any of the color image quality even after it has been pulled and stretched. This family of ink compositions transformed the garment industry by allowing the manufacturer to use any non-pretreated fabric at any scale, including in “roll-to-roll” printing machines (continuous substrate printing machines), while not sacrificing the color gamut and image resolution which have been previously achievable only by dye-based digital inks.